G main bearings

kwoods · Oct 31, 2017

Tearing a G down this winter, will probably replace the babbitted rods with 70 insert rods. Is there also insert type main bearings available or am I stuck with babbitted mains? With the addition of .125" over high compression pistons I'll be looking at around 10:1 compression, that's why I'm looking to replace the babbitted bearings.

buickanddeere · Oct 31, 2017

First time taking one of these apart . Send the cam out to have it ground to match the compression ratio and 93 octane pump gas.

Kent Petersen · Nov 1, 2017

AS you put it you are stuck with Babbitt mains you better check you rod journals ,they need to be near perfect to get inserts to stay in the tractor

kwoods · Nov 1, 2017

I'm probably going to end up pulling the crank and have it ground, #2 journal has some scarring. Figured I might as well while I have it apart.

Drew · Nov 1, 2017

Actually, there are a couple options for 1 piece bearings for your G. In reality, for what you are doing the babbit should be fine.

If your current bearings are totally trashed, JDparts shows new babbit shells available. Now how available they actually are, I don't know.

The last 2000'ish??? G tractors had 1 piece sleeve bearings like the number series tractors. Start beating the bushes and see if you can find a pair of main housings. NOTE: If you use the late 1 piece housings, you MUST get the timing gear off the crankshaft to match it. The gear for the 1 piece housing is a different width than the earlier babbit/2 piece bearing housing. Since your engine doesn't sound too wild, these housings should live. On a big engine, I have seen them crack.

Billet 1 piece main housings are available from Murphys. For what it sounds like you are doing, the only advantage to these would be a positive main seal instead of the OE type oil slinger.

farmer_nk · Nov 1, 2017

Manitowoc Motor Machine makes the 1 piece main bearings. http://www.motormachining.com/html/john_deere_main_bearings.html

kwoods · Nov 1, 2017

I feel like this project could become a slippery slope if I'm not careful. With my dad decking the head to the eyebrows and the high compression pistons this is going to become strictly a pulling tractor. This really wasn't the scope of this project before I realized the kind of compression I was going to get. My intentions were to add some horsepower and liven it up a little.

Buick, can you elaborate on how a different cam grind will allow for a lower octane gas? Is the goal to decrease the dynamic comp ratio?

More than likely I will stick with the babbit mains.

buickanddeere · Nov 1, 2017

there was no specific mention that this was going to be a dedicated pulling only tractor.
The cam duration and overlap can be ground to prevent high enough compression pressure to knock on 93 octane. Being a puller then tell the cam shop you are running 100LL or what ever.
This would also be the time for valve, seat, bowl, port, manifold and air cleaner work.

kwoods · Nov 1, 2017

Could I get away with keeping the stock cam profile? 10:1 comp is a rough estimate. The aluminum pistons will be about .200" from the top of the cylinder at TDC. I estimated the piston dish and head combustion chamber volumes. I plan on measuring fluid volume of the head this weekend to get a better number. I don't have the pistons so I can't measure the dish volume yet.

teddy52food · Nov 1, 2017

Make sure to tell the guy or gal doing the grinding to keep the right radius.

buickanddeere · Nov 2, 2017

Installing 10 to 1 pistons to make power and can’t have the cam ground and the followers trued up? The factory cam was speced with 4 to 1 compression and operating at 900rpm. Grinding the cam will work together with the compression instead of against it . Ask in the external_link on this site and from some cam grinding shops how much power that will be lost without a re-Grind to suit the application.

Kent Petersen · Nov 4, 2017

Once again B&D you prove that you don,t know what you are talking about the cam for a G is F900R the cam for a 70 Gas is an F900R so tell use how that can be

G main bearings

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